Spark plugs, gaps, etc., with Tri-Spark ignition

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Chris Larkin

Chris Larkin

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I have a 1973 850 Commando - I've installed a Tri-Spark ignition. Now to change out plugs. I plan to purchase resistor type plugs and seeing a lot of chatter about iridium types. Cost is an issue, kinda... but what's more important is reliability... eliminating future issues by installing best possible as a start point. May I have some recommendations, please. Also, what gap range is best suited for a Tri-Spark set up? I've set the Tri-Spark to fire at 28 degrees btdc Thank you.
 
I was running the NGK iridium at .028" on a wassell ignition and had the best plug life ever on my machine.... Perhaps 3K before they went TU.... Now have BPR 7ES in it, but haven't checked it out yet due to finishing up the GL project.
 
Plugs are cheap. I use NGK BPR7ES with .025 gap and change them out every 5-10k miles whether they need it or not. I also run a Trip-Spark.
Discussion about plugs on this forum can be like an oil thread. Some for and some against iridium. Those against cite high cost with no real
benefit. Some cite bad quality control and counterfeit NGKs on the market from eBay (know your supplier). Sometimes plugs are bad out of the box. Some claim Champion plugs to be superior to NGK. I've never been broken down at the side of the road due to plugs; Tri-Spark, yes ;) ). Plugs are cheap. Buy a half dozen and focus on other things like high quality high tension leads and caps, reed breather, decent rear shocks, etc.
 
lazyeye6 said:
Plugs are cheap. I use NGK BPR7ES with .025 gap and change them out every 5-10k miles whether they need it or not. I also run a Trip-Spark.
Discussion about plugs on this forum can be like an oil thread. Some for and some against iridium. Those against cite high cost with no real
benefit. Some cite bad quality control and counterfeit NGKs on the market from eBay (know your supplier). Sometimes plugs are bad out of the box. Some claim Champion plugs to be superior to NGK. I've never been broken down at the side of the road due to plugs; Tri-Spark, yes ;) ). Plugs are cheap. Buy a half dozen and focus on other things like high quality high tension leads and caps, reed breather, decent rear shocks, etc.
Click to expand...
Thank you very much!
 
My last set of Iridium plugs I replaced at 15,000 miles, not because they failed but because I thought I should. Most plugs fail because owners tend to run very rich. I installed an O2 sensor into my right hand down pipe a few years ago and tuned the carb based on the readings given. My plugs have just a bit of colour at the base. I get over 60 MPG. I encourage people to fit the gauge and sensor to find out what's really happening instead of going on somebody's recommendation.
 
The recommendation on this forum has been if using resistor plugs don’t use resistor caps. I have been running a Tri Spark for about four years. My ‘72 750 combat has BP7ES NGK plugs, NGK resistor caps and copper plug wires. Non resistor NGK plugs are supposedly no longer available, but I have a large enough stash to last a long time.
 
I have run the same NGK BP7ES plugs for over 45,000 miles in my combat and the only reason i replaced them was they looked like crap on the outside from rust.
 
I know I change my plugs unnecessarily early.

But then again, I also know that plugs degrade, they’re not a binary ‘work or don’t work’ kinda thing.

On a track, especially with a high compression motor, normal plugs might not last one day before you notice some misfiring at high rpm, or a performance loss, and that means they were losing performance way before you noticed. Iridium plugs avoid this.

Dyno runs show this, new plugs often give a higher reading, even if the old ones have only been in for a few runs and seem fine.

On the road, my thinking is that the above can translate into a small, incremental performance loss that the rider might not notice, but that adds up over time.

So, all in all, I’ll continue my ‘change ‘em early’ strategy.
 
I change the Norton's plugs in the same interval that I used to change the plugs in other bikes/muscle cars back in the same era - about 3000 miles. AND it was because they needed it! :) Much beyond that mileage and I would start to notice a lack of smoothness and some misfiring under load.

Contrast that to nowadays where the four cars we've owned since 2000 never had or needed new plugs while we owned them - max mileage was around 80,000 miles the others between 60-70. I have not needed/installed new plugs in any of our (relatively) current bikes - all 2014 or later.
 
As part of your service schedule check continuity with a multimeter. Either Ohms or use a battery and multimeter on V’s. They might look like they are sparking on the outside when you kick the bike over, inside under pressure probably not so good.
 
The gap is fixed on Iridiums, do not set the gap just put them in. If you damage the plug by setting the gap and insert it guess where that very small piece goes that could fall off. Just make sure you buy them from an outlet that the manufacturer recommends, fakes are hard to spot these days but with a genuine one in one hand and fake in the other the fake is easily spotted as it is much lighter.
 
I don't think I've ever had to change plugs because it needed it. Mine are getting rusty too. Running Champion N7YCs with NGK 5K Ohm plug caps, copper wires and a brand new Tri-Spark, previously Pazon Altair ignition.
 
my 2-cents on the subject - copper core plugs are around $2 each - swap them out with fresh ones at each oil change, 5K miles, or whatever - no muss, no fuss....
 
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…and another way at looking at this - plugs are cheap - $2 (each) X2 equals four bucks. you can't buy a decent cheeseburger for $4, and you poop that out the next day. a couple draft beers will cost you $4, and you'll pee those out within hours, so there absolutely no reason for not changing plugs frequently. to the best of my knowledge, NO plug manufacturer has a "high-mileage" award on their product. if there was, my son should get it for getting 190K miles out of the original delco iridiums in his 2011 camaro. I've always read that copper core plugs have the highest energy transfer, and I have no reason to doubt that. the biggest advantage by using the "exotic" core plugs is in longevity where the labor rate to change plugs in late models cars is cost prohibitive. lets face it, changing plugs is probably the easiest maintenance item done on the commando, so IMO, no advantage to using anything but copper core and changing them out as a regular maintenance item.
 
I have '74 850 with Dyna coils, Boyer ignition, copper core plug wires with non resistor plug caps. Have always used NGK BP7ES plugs account somewhere I read that not to use the resistor type plugs with this set up. I do not remember where I saw that information if on this forum or where. Anybody have accurate input on this. Now that the BP7ES plugs are not longer available and the auto parts places give you the resistor NGK's as NGK says this is the replacement. However they also say that NGKYR5 replaces the BP7. Any info on that? Thanks.
 
N
dennisht said:
I have '74 850 with Dyna coils, Boyer ignition, copper core plug wires with non resistor plug caps. Have always used NGK BP7ES plugs account somewhere I read that not to use the resistor type plugs with this set up.
Click to expand...
You can use resistor plugs or resistor caps but preferably not both, although analogue ignitions such as the Boyer Micro MkIII and MkIV don't require either to function but digital ignitions generally do.

"Why Do I Need To Use Suppressed Plug Caps?​

MKIII and MKIV do not require suppressed plug caps for operation although we recommend using supressed 5000 ohm plug caps. Micro Digital and Micro Power units must be fitted with supressed plug caps. Plug caps fitted with suppression resistors are usually fitted to prevent radio interference. Radio interference (noise) can cause more complex electronic circuits like radios and computers to malfunction."
 
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